This blog provides updated forecasts and comments on current weather or other topics

Friday, January 7, 2011

Historic Snowstorm This Week?

I have a lot to talk about.

Some of you have been commenting about the potential for a big event next week and the National Weather Service and the media have been hinting about it. I will analyze the possibility in this blog. Taken literally, the latest model runs based on the U.S. global modeling system suggest a major lowland snowstorm late on Wednesday and on Thursday. And lets be clear up front: the event is a long ways off (Wednesday/Thursday) and uncertainties are still large. Exactly who will get the most snow is not clear. Portland, SW Washington, Puget Sound? And in this blog I will discuss how we estimate and deal with the uncertainties.

Act I, the Cool Down: Lets begin with today. During the afternoon we had a marvelous cold frontal passage, with a large windshift from southerly to northerly, sharp pressure trough, and moderate rain. As the front passed by and the winds swung to northwesterly along the coast a nice Puget Sound convergence zone formed (see radar below), dampening the bicycle commute home for many.

Although temperatures are rapidly falling aloft, it is still way too warm for snow over the lowlands, and will continue to be too warm until tomorrow in most locations.

This is the first act of our little weather play.

Act II, The Tease: Colder air will move into British Columbia and Washington tomorrow and by tomorrow evening it will be cold enough to snow over the Puget Sound lowlands (even earlier in the day above 500 ft and where precipitation intensity is greatest). Later tomorrow cold northeasterly winds will start pushing southwestward through the Fraser River Gap. Several convergence bands will be established tomorrow and early Sunday and some scattered showers will also occur. Many of these showers will be snow. At most places it will be flurries and light, but in some of the convergence bands perhaps an inch or two will be possible. And Sequim and Port Angeles could get some upslope snow again. Very similar to a week ago. The models suggest that the Portland area could get some light snow on Sunday from a weak disturbance moving down the coast.

Act III: Waiting-Cold and Dry

As the cold air pushes south, the showers will end over northern Washington and the drying will push south during the day. By Monday, the region will be cold and dry. Temperatures Monday and Tuesday morning will drop back into the 20s and the the highs will only reach into the 30s. Sunny, but cold.

Act IV: Snowapocalypse?

The cold air will be in place and then a Pacific weather system will approach from the west and southwest, pushing moisture over the region...as snow north of the Oregon/Washington border. Here is a surface chart showing what the UW WRF model expects for Thursday morning at 4 AM:You can see the Pacific low pressure system off of southern/central Oregon and the cold air (blue colors over Washington). Cold air will be moving into NW WA through the Fraser Gap and over lower terrain at this time. Precipitation will move into Oregon late on Wednesday and snow will extend northward. Here is the snowfall for the 24h period ending 4 AM on Thursday. Eastern Oregon and the Cascades down into the foothills get snow. Portland gets snow as does southern WA.

The snow will then extend northward. Here is the next 24-h:

Several inches of snow gets to Seattle, but the heaviest stuff is to the south, with roughly a foot in the Portland area and roughly half a foot to Olympia. The previous run had the heaviest snow over Seattle. This is all followed by snow showers and continued cold.

Bottom line: Although each run is a little different in low intensity and position, all have the same general solution with some area in the NW lowlands being hit by significant snow. These are all based on the American GFS (Global Forecast System) model, downscaled with the high-resolution WRF model. The European Center Model, which is generally superior to the GFS, takes the low north of us and we get rain.So does the Canadian GEM model.The weather will crucially depend on the position of the low--if it goes north of us we get rain, just south of us, a big snowstorm, too far south, nothing. We need to wait to really know what is going to happen. Hopefully, by Monday the solutions will pull together and our confidence in an evolution will increase.

Anyone have a good site to view the Euro Model? I usually watch the NWS site for the GFS and the NAM. When I search for the Ruo model it is always a low resolution model with not much detail and very difficult to read. Thanks in advance.

I`m rather skeptical about a major snowstorm for several reasons.First, the upper level heights are rather high(530-540 MBs+)to support a snow situation.I`d feel a lot more favor in snow if the heights can dip into the 520 to 525 range here by midweek.(The 500 MB height here in last November`s snowstorm was about 515, by the way.)Secondly,in past historic snowstorms, there`s usually been a major arctic air outbreak funnelling down the Fraser with winds at Bellingham at 30 to 40 MPH with gusts of 50 to 60 or more.This due to a Williams Lake BC to Bellingham pressure gradient somewhere around 15MB or more.I haven`t seen any indication of this kind of strong outbreak on any discussion or map so far.And finally, the whole event comes down to the trajectory of the approaching low.If the low doesn`t move inland just to the south of here, preferably near the mouth of the Columbia river the storm will be a dud--even if the upper lever heights are low and a strong Fraser outflow is present.Specifics on the storm track has been very vague so far.So, I would have to conclude that the odds are are against a major snowstorm--at least for now.Maybe the situation will change in a few days.....

Thank you Dr Mass . I always appreciate your careful explanations. I am gaining a good understanding of how the technology is used. After reading this I feel comfortable about some of my planning for the week ahead.

As usual, a careful and measured response, highly informative and without any hint of "mass (no pun intended) hysteria and panic."Your blog is a joy, and it's one of the few I regularly check. Thanks so much for your insights and education. I always look forward to your discussions.

The NAM has the low coming north later next week, the big difference looks to be the strength of the high between the GFS and the NAM. I have a hard time believing the NAM right now just because the strength of the arctic high over the continent, the low should track around the periphery of the arctic air. Maybe the strength of the high is being well overdone??

12GFS shifts the low further to the N into SW WA...This would mean at least 10+ inches for Seattle...Also worth noting - 12Z GFS paints a snowy pattern through 1/19...Guess LA NINA is beginning to make her mark on W WA!

I know 2 kids who are hoping for a snowpocalypse next week! They had 2.5 days off school extending their Thanksgiving becuz of the Nov. event. We're at about 700', east of North Bend in the foothills. We ended up with about an inch of the stuff last night in about 30 minutes and the frost line at this point looks to be about 1500'. NWS is still predicting that we are due for another 1-3" this afternoon, 1-2" tonight, and 1-2" tomorrow, never mind next week. BRING IT ON!

Where are the subfreezing daytime highs? All I see are mid and even upper 30s. I am skeptical about getting dry cold snow like we had in November. If we are going to get wet snow, I'd rather it be rain.

A few years ago when we had our big windstorm, five out of nine of the UW ensemble members (that were available at that time) had a big windstorm with a perfect set up. That was very good agreement and made the forecast pretty straitforward. It will be a great help to watch the surface low development and tracks in the ensembles next week. The members are CENT / GFS / CMCG / ETA / GASP / JMA / NGPS / TCWB / UKMO / GFS+ / CMCG+ / GASP+ / JMA+ / UKMO+ ETA+ / NGPS+ / TCWB+ /

Now I should know this, but is one of the members the same or a close match to the ECMWF?

After reading the opening paragraph, I was waiting to find out how you "estimate and deal with the uncertainties," but I never saw how. I was waiting for an explanation about how you determine which case(s) may be the most likely, and so on. Isn't there something meteorologically that will influence where the low will go? Or do forecasters just wait until the models agree to tell us what they agree on?

It requires an amazing amount of accuracy for the models to nail this one so far out. The storm that is going to hit us is still about 2,000 miles out in the Pacific. If the center of the low shifts 100 miles north or south of making landfall around Long Beach it is the difference between a giant snowstorm or rainstorm. It is a 20 degree swing in temps. Absolutely crazy! One thing is for sure there is going to be lots of moisture coming our way and it might be snow or it might be rain, but someone on the west coast from Vancouver to Portland is going to get lots of snow. Love it!

I have to agree with Josh.The latest 00z Jan 9th models seem to be trending with warmer weather midweek for this area.And usually when they trend warmer, they seldom ever flip flop back to the cold and snowy weather scenario.It looks like the upper level trough that was originally was forecast to dip south into our area will be moving more west than south.Of course, we all know that means a mild maritme westerly flow here.(Maybe the Bellingham area still has a chance for snow ,provided that the arctic outflow continues and enough Pacific moisture overruns it.)I suspect that the winter weather advisories for next week will soon be toned down or cancelled completely.I`m eagerly waiting for Prof. Mass`analysis of the situation.

if this is going to be a repeat of the 2004 event, it will be nice because during the last one I just got home from the UW hospital after major surgery and was in a oxycodone haze: I do not remember anything at all!!!

Bellingham is back in the winter wonderland for the time being. When I was up briefly at 1:30 am there were huge wet flakes falling thickly. This morn it looks like maybe one or two inches wioth a slight chance of more. Love it!